There are two different methods for making panels herein contemplated, both of which result in a somewhat similar panel construction. The difference is that one method is capable of building into the panel more softness by including larger amounts of foamed material. Basically, this softer configuration is used in the more expensive luxury cars, whereas the other method is used basically in the large majority of other vehicles.
The method of making the luxury panel is essentially a two-stage process. In the first stage of the process, a substrate which is in the form of the panel is made by placing a fiberglass reinforcing mat in the lower half of a two-part mold and then filling the lower half of the mold with a foamable material such as liquid polyurethane capable of being cured into a foamed condition. After the foamable material has been inserted into the lower half of the mold, the upper half is moved down and then the foamable material is cured under heat to complete the substrate which is fairly rigid. In the second stage of the process, the substrate molded in the first stage is placed in the upper half of a second two-part mold. The lower part of the mold is in essence a vacuum mold. The second stage procedure is begun by moving a heated sheet of imperforate vinyl over the bottom part of the mold and then drawing by vacuum the heated sheet into the mold so that the three-dimensional configuration is formed on the vinyl. After the vinyl has been moved into engagement with the mold by the vacuum source, an amount of foamable material such as liquid polyurethane is then injected into the mold on top of the vinyl and thereafter the upper part of the mold which contains the substrate is then moved into cooperating relation with the lower part and the foamable material is cured into a relatively soft foamed condition.
The other more economical process is essentially a one-stage process which utilizes a two-part mold, the lower part of which again is a vacuum mold for the vinyl exterior sheet of the door panel to be made. In this case, the vinyl comes as the outer layer of a laminate which includes a layer of foamed material bounded thereto. The laminate is initially heated and then vacuum-drawn into the lower part of the mold. Next, a mat of fiberglass or similar reinforcing is placed inside the laminate vacuum adhered to the lower mold and, thereafter, a liquid polyurethane is added to the lower mold part over the vacuum-held laminate. The upper mold part is then closed and essentially a relatively rigid substrate is molded integrally with the vinyl laminate. In this process, it is not possible to provide much thickness and softness in the foam that is laminated with the vinyl or at least not as much as can be used in the second step of the two step process.
In the methods for making vehicle door panels herein contemplated, it has been the most widely accepted practice to make the door panels without bolsters and then add the bolsters to the panels after the vehicle panels have been made.
In both processes, the door panel that is made usually has a bolster added thereto in the area between the window sill portion and the arm rest portion and a rug section may be added to the lower portion below the arm rest portion. The bolster normally has a textile exterior mounted on a relatively rigid carrier. The bolster thus constructed must be adhered to the panel and must be edged in some fashion, often by a marginal trim strip or the like.
The addition of a bolster is so highly desirable from a decorative standpoint that the costs incident to its carrier construction and the necessity to adhere the bolster construction in place and to edge it somehow have generally been accepted. Nevertheless, there have been efforts undertaken to make the provision of one or more bolsters on a door panel more cost effective. Examples of various proposals are disclosed in the following U.S. Pat. Nos.: 4,740,417, 4,766,025, 4,923,539, and 5,091,031. Japanese patent publications 63-176132 and 62-211128 also provide examples.
The patent literature has suggested a procedure by which a trim insert is incorporated into the door panel during formation of the panel in a mold apparatus. For example, U.S. Pat. No. 4,923,539 discloses a molding method in which a textile insert is laminated onto a vinyl cover film with aid of nesting die. It is further disclosed that an adhesive is applied between the insert and the vinyl film to adheringly secure the vinyl to the insert. While a method of manufacturing a door panel in such fashion is more cost effective than the method in which an insert is added to the door panel after the panel has been made, the quality of the finished product and the cost-effectiveness of the method has been limited. More particularly, use of an unspecified adhesive to adhere the bolster material to the vinyl material may cause plasticizer migration between the vinyl and the adhesive, and resultant degradation of both. In addition, when an adhesive with a melting point which is too high is used, the adhesive will not be activated (become tacky) upon contact with the heated vinyl. If, on the other hand, the temperature activation range of the adhesive is too low, the adhesive may disintegrate before a temperature sufficient to soften vinyl and/or bolster material is reached. If the vinyl and/or bolster is not softened to the extent necessary, the desired amount of grain imprint therein will not be achieved, and part detail will be lost. Finally, if the thickness of the adhesive used is insufficient, the adhesive will not adequately perform its bonding function, nor will its imperforate nature be adequately employed to enable the porous textile outer layer of the bolster to be moved into conformity with a mold surface and retained therein by a vacuum communicated through openings in the mold surface. If the thickness of adhesive is greater than what is necessary, on the other hand, the expense associated with providing the adhesive will accordingly be unnecessarily high. Thus, there still exists a need to make the provision of a bolster on a door panel with optimized quality and cost-effectiveness.